This image is a composite of separate exposures acquired by the WFC3 instrument on HST. Several filters were used to sample broad wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are:

The composite image at left, taken in visible and near-infrared light, reveals the location of five tiny galaxies clustered together 13.1 billion light-years away. The circles pinpoint the galaxies.

The sharp-eyed Wide Field Camera 3 aboard NASA's Hubble Space Telescope spied the galaxies in a random sky survey. The developing cluster is the most distant ever observed. The young galaxies lived just 600 million years after the universe's birth in the big bang.

The average distance between them is comparable to that of the galaxies in the Local Group, consisting of two large spiral galaxies, the Milky Way and Andromeda, and a few dozen small dwarf galaxies.

The close-up images at right, taken in near-infrared light, show the puny galaxies. The letters "a" through "e" correspond to the galaxies' location in the wide-field view at left. Simulations show that the galaxies will eventually merge and form the brightest central galaxy in the cluster, a giant elliptical similar to the Virgo cluster's M87.

Galaxy clusters are the largest structures in the universe, comprising hundreds to thousands of galaxies bound together by gravity. The developing cluster presumably will grow into a massive galactic city, similar in size to the nearby Virgo cluster, a collection of more than 2,000 galaxies.